SOME AQUATIC WORMS, ETC. 177 



rigid setae. The dorsal spines are always in two trans- 

 verse rows, but the number varies from four in each to 

 three in one and five in the other. They are unequally 

 furcate. 



11. CH^ETONOTUS ACANTHODES. 



The upper surface of this form is wondrously well 

 protected. It possesses both spines and scales, the lat- 

 ter imbricated, and their somewhat pointed free margins 

 directed forward, each one bearing a small supplement- 

 ary scale or scale-like thickening on its posterior part, 

 from which springs a recurved, unequally furcate spine. 

 Near the body-centre the dorsal surface is traversed by 

 a series of large stout spines rising obliquely upward 

 and backward, and forming a kind of spinous hedge, 

 the surface behind these appendages bearing few small 

 conical thorns or none. The body margins are fringed 

 by short spines. The central space on the ventral as- 

 pect between the two longitudinal, lateral bands of cilia, 

 is beset with short, fine, recurved prickles, and five or 

 more long bristles project from the same surface beyond 

 the border of the posterior bifurcation, while on each 

 side of the body near the posterior extremity there are 

 two large recurved spines. The animal is usually found 

 among Sphagnum. 



12. Cn^ETONOTUS SPfNIFER. 



Among Riccia and Lemna in shallow ponds this 

 well-armored form is not rare. The upper surface is 

 covered by rounded imbricated scales, the free margins 



